Commercial service of a wideband code division multiple access (W-CDMA) system among so-called third-generation communication systems has been offered in Japan since 2001. In addition, high speed downlink packet access (HSDPA) service for achieving higher-speed data transmission using a downlink has been offered by adding a channel for packet transmission (high speed-downlink shared channel (HS-DSCH)) to the downlink (dedicated data channel, dedicated control channel). Further, in order to increase the speed of data transmission in an uplink direction, service of a high speed uplink packet access (HSUPA) system has been offered. W-CDMA is a communication system defined by the 3rd generation partnership project (3GPP) that is the standard organization regarding the mobile communication system, where the specifications of Release 10 version are produced.
Further, new communication systems referred to as long term evolution (LTE) regarding radio areas and system architecture evolution (SAE) regarding the overall system configuration including a core network (merely referred to as network as well) as communication systems independent of W-CDMA is studied in 3GPP. This communication system is also referred to as 3.9 generation (3.9 G) system.
In the LTE, an access scheme, a radio channel configuration and a protocol are totally different from those of the current W-CDMA (HSDPA/HSUPA). For example, as to the access scheme, code division multiple access is used in the W-CDMA, whereas in the LTE, orthogonal frequency division multiplexing (OFDM) is used in a downlink direction and single career frequency division multiple access (SC-FDMA) is used in an uplink direction. In addition, the bandwidth is 5 MHz in the W-CDMA, while in the LTE, the bandwidth can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz per base station. Further, differently from the W-CDMA, circuit switching is not provided but a packet communication system is only provided in the LTE.
The LTE is defined as a radio access network independent of the W-CDMA network because its communication system is configured by a new core network different from a core network (general packet radio service: GPRS) of the W-CDMA. Therefore, for differentiation from the W-CDMA communication system, a base station that communicates with a user equipment (UE) and a radio network controller that transmits/receives control data and user data to/from a plurality of base stations are referred to as an E-UTRAN NodeB (eNB) and an evolved packet core (EPC) or access gateway (aGW), respectively, in the LTE communication system.
Unicast service and evolved multimedia broadcast multicast service (E-MBMS service) are provided in this LTE communication system. The E-MBMS service is broadcast multimedia service, which is merely referred to as MBMS in some cases. Bulk broadcast contents such as news, weather forecast and mobile broadcast are transmitted to a plurality of user equipments. This is also referred to as point to multipoint service.
Non-Patent Document 1 (Chapter 4) describes the current decisions by 3GPP regarding an overall architecture in the LTE system. The overall architecture is described with reference to FIG. 1. FIG. 1 is a diagram illustrating the configuration of the LTE communication system. With reference to FIG. 1, the evolved universal terrestrial radio access (E-UTRAN) is composed of one or a plurality of base stations 102, provided that a control protocol for a user equipment 101 such as a radio resource control (RRC) and user planes such as a packet data convergence protocol (PDCP), radio link control (RLC), medium access control (MAC) and physical layer (PHY) are terminated in the base station 102.
The base stations 102 perform scheduling and transmission of a paging signal (also referred to as paging messages) notified from a mobility management entity (MME) 103. The base stations 102 are connected to each other by means of an X2 interface. In addition, the base stations 102 are connected to an evolved packet core (EPC) by means of an S1 interface. More specifically, the base station 102 is connected to the mobility management entity (MME) 103 by means of an S1_MME interface and connected to a serving gateway (S-GW) 104 by means of an S1_U interface.
The MME 103 distributes the paging signal to a plurality of or a single base station 102. In addition, the MME 103 performs mobility control of an idle state. When the user equipment is in the idle state and an active state, the MME 103 manages a list of tracking areas.
The S-GW 104 transmits/receives user data to/from one or a plurality of base stations 102. The S-GW 104 serves as a local mobility anchor point in handover between base stations. Moreover, a PDN gateway (P-GW) is provided in the EPC, which performs per-user packet filtering and UE-ID address allocation.
The control protocol RRC between the user equipment 101 and the base station 102 performs broadcast, paging. RRC connection management and the like. The states of the base station and the user equipment in RRC are classified into RRC_Idle and RRC_CONNECTED. In RRC_IDLE, public land mobile network (PLMN) selection, system information (SI) broadcast, paging, cell re-selection, mobility and the like are performed. In RRC_CONNECTED, the user equipment has RRC connection, is capable of transmitting/receiving data to/from a network, and performs, for example, handover (HO) and measurement of a neighbor cell.
The current decisions by 3GPP regarding the frame configuration in the LTE system described in Non-Patent Document 1 (Chapter 5) are described with reference to FIG. 2. FIG. 2 is a diagram illustrating the configuration of a radio frame used in the LTE communication system. With reference to FIG. 2, one radio frame is 10 ms. The radio frame is divided into ten equally sized subframes. The subframe is divided into two equally sized slots. The first and sixth subframes contain a downlink synchronization signal (SS) per each radio frame. The synchronization signals are classified into a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).
Multiplexing of channels for multimedia broadcast multicast service single frequency network (MBSFN) and for non-MBSFN is performed on a per-subframe basis. MBSFN transmission is a simulcast transmission technique realized by simultaneous transmission of the same waveforms from a plurality of cells. The MBSFN transmission from a plurality of cells in the MBSFN area is seen as a single transmission by a user equipment. The MBSFN is a network that supports such MBSFN transmission. Hereinafter, a subframe for MBSFN transmission is referred to as MBSFN subframe.
Non-Patent Document 2 describes a signaling example when MBSFN subframes are allocated. FIG. 3 is a diagram illustrating the configuration of the MBSFN frame. With reference to FIG. 3, a radio frame including the MBSFN subframes is allocated per radio frame allocation period. The MBSFN subframe is a subframe allocated for the MBSFN in a radio frame defined by the allocation period and the allocation offset (radio frame allocation offset), and serves to transmit multimedia data. The radio frame satisfying Equation (1) below is a radio frame including the MBSFN subframes.SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset  (1)
The MBSFN subframe is allocated with six bits. The leftmost bit defines the MBSFN allocation for the second subframe (#1). The second bit, third bit, fourth bit, fifth bit, and sixth-bit define the MBSFN allocation for the third subframe (#2), fourth subframe (#3), seventh subframe (#6), eighth subframe (#7), and ninth subframe (#8), respectively. The case where the bit indicates “one” represents that the corresponding subframe is allocated for the MBSFN.
Non-Patent Document 1 (Chapter 5) describes the current decisions by 3GPP regarding the channel configuration in the LTE system. It is assumed that the same channel configuration is used in a closed subscriber group cell. (CSG cell) as that of a non-CSG cell. Physical channels are described with reference to FIG. 4. FIG. 4 is a diagram illustrating physical channels used in the LTE communication system.
With reference to FIG. 4, a physical broadcast channel (PBCH) 401 is a downlink channel transmitted from the base station 102 to the user equipment 101. A BCH transport block is mapped to four subframes within a 40 ms interval. There is no explicit signaling indicating 40 ms timing. A physical control format indicator channel (PCFICH) 402 is transmitted from the base station 102 to the user equipment 101. The PCFICH notifies the number of OFDM symbols used for PDCCHs from the base station 102 to the user equipment 101. The PCFICH is transmitted in each subframe.
A physical downlink control channel (PDCCH) 403 is a downlink channel transmitted from the base station 102 to the user equipment 101. The PDCCH notifies the resource allocation of DL-SCH (downlink shared channel that is one of the transport channels shown in FIG. 5 described below) and PCH (paging channel that is one of the transport channels shown in FIG. 5), and HARQ information related to DL-SCH. The PDCCH carries an uplink scheduling grant. The PDCCH carries acknowledgement (Ack)/negative acknowledgement (Nack) that is a response signal to uplink transmission. The PDCCH is referred to as an L1/L2 control signal as well.
A physical downlink shared channel (PDSCH) 404 is a downlink channel transmitted from the base station 102 to the user equipment 101. A DL-SCH (downlink shared channel) that is a transport channel and a PCH that is a transport channel are mapped to the PDSCH. A physical multicast channel (PMCH) 405 is a downlink channel transmitted from the base station 102 to the user equipment 101. A multicast channel (MCH) that is a transport channel is mapped to the PMCH.
A physical uplink control channel (PUCCH) 406 is an uplink channel transmitted from the user equipment 101 to the base station 102. The PUCCH carries Ack/Nack that is a response signal to downlink transmission. The PUCCH carries a channel quality indicator (CQI) report. The CQI is quality information indicating the quality of received data or channel quality. In addition, the PUCCH carries a scheduling request (SR). A physical uplink shared channel (PUSCH) 407 is an uplink channel transmitted from the user equipment 101 to the base station 102. A UL-SCH (uplink shared channel that is one of the transport channels shown in FIG. 5) is mapped to the PUSCH.
A physical hybrid ARQ indicator channel (PHICH) 408 is a downlink channel transmitted from the base station 102 to the user equipment 101. The PHICH carries Ack/Nack that is a response to uplink transmission. A physical random access channel (PRACH) 409 is an uplink channel transmitted from the user equipment 101 to the base station 102. The PRACH carries a random access preamble.
A downlink reference signal is a known symbol in a mobile communication system. The physical layer measurement objects of a user equipment include reference symbol received power (RSRP).
The transport channels described in Non-Patent Document 1 (Chapter 5) are described with reference to FIG. 5. FIG. 5 is a diagram illustrating transport channels used in the LTE communication system. FIG. 5(A) shows mapping between a downlink transport channel and a downlink physical channel. FIG. 50(B) shows mapping between an uplink transport channel and an uplink physical channel.
Downlink transport channels are described. A broadcast channel (BCH) is broadcast to the entire coverage of a base station (cell). The BCH is mapped to the physical broadcast channel (PBCH).
Retransmission control according to a hybrid ARQ (HARQ) is applied to a downlink shared channel (DL-SCH). The DL-SCH enables broadcast to the entire coverage of the base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. The semi-static resource allocation is also referred to as persistent scheduling. The DL-SCH supports discontinuous reception (DRX) of a user equipment for enabling the user equipment to save power. The DL-SCH is mapped to the physical downlink shared channel (PDSCH).
The paging channel (PCH) supports DRX of the user equipment for enabling the user equipment to save power. The PCH is required to broadcast to the entire coverage of the base station (cell). The PCH is mapped to physical resources such as the physical downlink shared channel (PDSCH) that can be used dynamically for traffic.
The multicast channel (MCH) is used for broadcast to the entire coverage of the base station (cell). The MCH supports SFN combining of MBMS service (MTCH and MCCH) in multi-cell transmission. The MCH supports semi-static resource allocation. The MCH is mapped to the PMCH.
Retransmission control according to a hybrid ARQ (HARQ) is applied to an uplink shared channel (UL-SCH). The UL-SCH supports dynamic or semi-static resource allocation. The UL-SCH is mapped to the physical uplink shared channel (PUSCH).
A random access channel (RACH) shown in FIG. 5(B) is limited to control information. The RACH involves a collision risk. The RACH is mapped to the physical random access channel (PRACH).
The HARQ is described. The HARQ is the technique for improving the communication quality of a channel by combination of automatic repeat request and error correction (forward error correction). The HARQ has an advantage that error correction functions effectively by retransmission even for a channel whose communication quality changes. In particular, it is also possible to achieve further quality improvement in retransmission through combination of the reception results of the first transmission and the reception results of the retransmission.
An example of the retransmission method is described. In a case where the receiver fails to successfully decode the received data, in other words, in a case where a cyclic redundancy check (CRC) error occurs (CRC=NG), the receiver transmits “Nack” to the transmitter. The transmitter that has received “Nack” retransmits the data. In a case where the receiver successfully decodes the received data, in other words, in a case where a CRC error does not occur (CRC=OK), the receiver transmits “AcK” to the transmitter. The transmitter that has received “Ack” transmits the next data.
Examples of the HARQ system include chase combining. In chase combining, the same data is transmitted in the first transmission and retransmission, which is the system for improving gains by combining the data of the first transmission and the data of the retransmission in retransmission. This is based on the idea that correct data is partially included even if the data of the first transmission contains an error, and highly accurate data transmission is enabled by combining the correct portions of the first transmission data and the retransmission data. Another example of the HARQ system is incremental redundancy (IR). The IR is aimed to increase redundancy, where a parity bit is transmitted in retransmission to increase the redundancy by combining the first transmission and retransmission, to thereby improve the quality by an error correction function.
Logical channels described in Non-Patent Document 1 (Chapter 6) are described with reference to FIG. 6. FIG. 6 is a diagram illustrating logical channels used in an LTE communication system. FIG. 6(A) shows mapping between a downlink logical channel and a downlink transport channel. FIG. 6(B) shows mapping between an uplink logical channel and an uplink transport channel.
A broadcast control channel (BCCH) is a downlink channel for broadcast system control information. The BCCH that is a logical channel is mapped to the broadcast channel (BCH) or downlink shared channel (DL-SCH) that is a transport channel.
A paging control channel (PCCH) is a downlink channel for transmitting changes of the paging information and system information. The PCCH is used when the network does not know the cell location of a user equipment. The PCCH that is a logical channel is mapped to the paging channel (PCH) that is a transport channel.
A common control channel (CCCH) is a channel for transmission control information between user equipments and a base station. The CCCH is used in a case where the user equipments have no RRC connection with the network. In a downlink direction, the CCCH is mapped to the downlink shared channel (DL-SCH) that is a transport channel. In an uplink direction, the CCCH is mapped to the uplink shared channel (UL-SCH) that is a transport channel.
A multicast control channel (MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used for transmission of MBMS control information for one or several MTCHs from a network to a user equipment. The MCCH is used only by a user equipment during reception of the MBMS. The MCCH is mapped to the multicast channel (MCH) that is a transport channel.
A dedicated control channel (DCCH) is a channel for point-to-point transmission of the dedicated control information between a user equipment and a network. The DCCH is used when a user equipment is in RRC connection. The DCCH is mapped to the uplink shared channel (UL-SCH) in uplink and mapped to the downlink shared channel (DL-SCH) in downlink.
A dedicated traffic channel (DTCH) is a point-to-point communication channel for transmission of the user information to a dedicated user equipment. The DTCH exists in uplink as well as downlink. The DTCH is mapped to the uplink shared channel (UL-SCH) in uplink and mapped to the downlink shared channel (DL-SCH) in downlink.
A multicast traffic channel (MTCH) is a downlink channel for traffic data transmission from a network to a user equipment. The MTCH is a channel used only by a user equipment during reception of the MBMS. The MTCH is mapped to the multicast channel (MCH).
GCI represents a global cell identity. A closed subscriber group cell (CSG cell) is introduced in the LTE, long term evolution advanced (LTE-A) described below, and universal mobile telecommunication system (UMTS). The CSG is described below (see Chapter 3.1 of Non-Patent Document 3). The closed subscriber group cell (CSG cell) is a cell in which subscribers who are allowed to use are specified by an operator (hereinafter, referred to as “cell for specific subscribers” in some cases).
The specified subscribers are allowed to access one or more cells of a public land mobile network (PLMN). One or more cells in which the specified subscribers are allowed access are referred to as “CSG cell(s)”. Note that access is restricted in the PLMN. The CSG cell is part of the PLMN that broadcasts a specific CSG identity (CSG ID; CSG-ID) and broadcasts “TRUE” by CSG indication. The authorized members of the subscriber group who have registered in advance access the CSG cells using the CSG-ID that is the access permission information.
The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDs exist in a mobile communication system. The CSG-IDs are used by user equipments (UEs) for making access from CSG-related members easier.
The locations of user equipments are tracked based on an area composed of one or more cells. The locations are tracked for enabling tracking of the locations of user equipments and calling (calling of user equipments) even in an idle state. An area for tracking locations of user equipments is referred to as a tracking area.
A CSG whitelist is a list that may be stored in a universal subscriber identity module (USIM) in which all CSG IDs of the CSG cells to which the subscribers belong are recorded. The CSG whitelist is merely referred to as whitelist or is referred to as an allowed CSG list in some cases. The MME performs access control for the UEs accessing through CSG cells (see Chapter 4.3.1.2 of Non-Patent Document 9). Specific examples of the access by user equipments include attach, combined attach, detach, service request, and tracking area update procedure (see Chapter 4.3.1.2 of Non-Patent Document 9).
Service types of a user equipment in an idle state are described below (see Chapter 4.3 of Non-Patent Document 3). The service types of a user equipment in an idle state are classified into a limited service (also referred to as closed service), a normal service, and an operator service. The limited service includes emergency calls, an earthquake and tsunami warning system (ETWS), and a commercial mobile alert system (CMAS) on an acceptable cell described below. The normal service (also referred to as standard service) is the service for public use on a suitable cell described below. The operator service is the service for operators only on a reserved cell described below.
A “suitable cell” is described below. The “suitable cell” is a cell on which a UE may camp to obtain a normal service. Such a cell shall fulfill the following conditions (1) and (2).
(1) The cell is part of the selected PLMN or the registered PLMN, or part of the PLMN of an “equivalent PLMN list”.
(2) According to the latest information provided by a non-access stratum (NAS), the cell shall further fulfill the following conditions (a) to (d):
(a) the cell is not a barred cell;
(b) the cell is part of a tracking area (TA), not part of the list of “forbidden LAs for roaming”, where the cell needs to fulfill (1) above;
(c) the cell shall fulfill the cell selection criteria; and
(d) for a cell specified as CSG cell by system information (SI), the CSG-ID is part of a “CSG whitelist” of the UE (contained in the CSG whitelist of the UE).
An “acceptable cell” is described below. This is the cell on which a UE may camp to obtain limited service. Such a cell shall fulfill all the requirements of (1) and (2) below.
(1) The cell is not a barred cell. (2) The cell fulfills the cell selection criteria.
“Barred cell” is shown in the system information. “Reserved cell” is shown in the system information.
“Camping on a cell” represents the state where a UE has completed the cell selection/reselection process and the UE has selected a cell for monitoring the system information and paging information. A cell on which the UE camps is referred to as “serving cell” in some cases.
Base stations referred to as Home-NodeB (Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB) are studied in 3GPP. HNB/HeNB is a base station for, for example, household, corporation or commercial access service in UTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes of the access to the HeNB and HNB. Specifically, those are an open access mode, a closed access mode and a hybrid access mode.
The respective modes have the following characteristics. In the open access mode, the HeNB and HNB are operated as a normal cell of a normal operator. In the closed access mode, the HeNB and HNB are operated as a CSG cell. The CSG cell is a cell where only CSG members are allowed access. In the hybrid access mode, non-CSG members are allowed access at the same time. In other words, a cell in the hybrid access mode (also referred to as hybrid cell) is the cell that supports both the open access mode and the closed access mode.
According to 3GPP, there is a range of PCIs in all physical cell identities (PCIs), which is reserved by the network for use by CSG Cells (see Chapter 10.5.1.1 of Non-Patent Document 1). Splitting the range of PCIs is referred to PCI-split at times. The PCI split information is broadcast in the system information from the base station to the user equipments being served thereby. Non-Patent Document 5 discloses the basic operation of a user equipment using PCI split. The user equipment that does not have the PCI split information needs to perform cell search using all PCIs, for example, using all 504 codes. On the other hand, the user equipment that has the PCI split information is capable of performing cell search using the PCI split information.
Further, specifications standard of long term evolution advanced (LTE-A) as Release 10 are pursued in 3GPP (see Non-Patent Document 6 and Non-Patent Document 7).
As to the LTE-A system, it is studied that a relay and a relay node (RN) are supported for achieving a high data rate, high cell-edge throughput, new coverage area, and the like. The relay node is wirelessly connected to the radio-access network via a donor cell (Donor eNB; DeNB). The network (NW)-to-relay node link shares the same frequency band (hereinafter, referred to as “frequency band” in some cases) with the network-to-UE link within the range of the donor cell. In this case, the UE in Release 8 can also be connected to the donor cell. The link between a donor cell and a relay node is referred to as a backhaul link, and the link between the relay node and the UE is referred to as an access link.
As the method of multiplexing a backhaul link in frequency division duplex (FDD), the transmission from DeNB to RN is carried out in a downlink (DL) frequency band, and the transmission from RN to DeNB is carried out in an uplink (UL) frequency band. As the method of dividing resources in relays, a link from DeNB to RN and a link from RN to UE are time-division multiplexed in one frequency band, and a link from RN to DeNB and a link from UE to RN are also time-division multiplexed in one frequency band. This enables to prevent, in a relay, the transmission of the relay from interfering with the reception of the own relay.
Not only a normal eNB (macro cell) but also so-called local nodes such as pico eNB (pico cell). HeNB (HNB. CSG cell), node for hotzone cells, relay node, remote radio head (RRH) and repeater are studied in 3GPP. The network composed of various types of cells as described above is also referred to as a heterogeneous network (HetNet) in some cases.
The frequency bands (hereinafter, referred to as “operating bands” in some cases) usable for communication have been predetermined in the LTE. Non-patent Document 8 describes the frequency bands. In the frequency division duplex (FDD) communication, a frequency band for downlink (hereinafter, referred to as “downlink frequency band” in some cases) and a frequency band for uplink (hereinafter, referred to as “uplink frequency band” in some cases) that is paired with the downlink frequency band have been predetermined, where the uplink frequency band differs from the downlink frequency band. This is because the downlink and uplink are necessarily required for conventional communication such as voice communication so that transmission/reception are enabled at the same time by splitting the frequencies between downlink and uplink in the FDD.
In the FDD, a default value of an interval (TX-RX frequency separation) between a carrier frequency of resources for use in downlink (hereinafter, referred to as “downlink carrier frequency” in some cases) and a carrier frequency of resources for use in uplink (hereinafter, referred to as “uplink carrier frequency” in some cases) is determined per frequency band. Non-Patent Document 8 describes a default value at the TX-RX frequency separation.
In the LTE, a cell broadcasts, to UEs being served thereby, the frequency band information and uplink carrier frequency deployed by the own cell as broadcast information. Specifically, the frequency band information is included in the SIB1. The uplink carrier frequency is included in the SIB2. In a case where the uplink carrier frequency is not included in the SIB2, the uplink carrier frequency is derived from the downlink carrier frequency using the default value at the TX-RX frequency separation. The UE is capable of recognizing the downlink carrier frequency through cell selection or reselection and is capable of obtaining the frequency band and uplink carrier frequency deployed by the cell through reception of the broadcast information from the cell.
As disclosed in Non-Patent Document 1, the development of “long term evolution advanced (LTE-A)” specifications as Release 10 is pursued in 3GPP.
Carrier aggregation (CA) is studied in the LTE-A system, in which two or more component carriers (CCs) are aggregated to support wider transmission bandwidths up to 100 MHz.
A Release 8 or 9-compliant UE, which supports LTE, is capable of transmission/reception on only the CC corresponding to one serving cell. On the other hand, it is conceivable that a Release 10-compliant UE may have the capability of transmission/reception, only reception, or only transmission on the CCs corresponding to a plurality of serving cells at the same time.
Each CC employs the configuration of Release 8 or 9, and the CA supports contiguous CCs, non-contiguous CCs, and CCs in different frequency bandwidths. The UE cannot configure the number of uplink CCs (UL CCs) equal to or more than the number of downlink CCs (DL CCs). The CCs configured by the same eNBs do not need to provide the same coverage. The CC is compatible with Release 8 or 9.
In CA, an independent HARQ entity is provided per serving cell in uplink as well as downlink. A transport block is generated per TTI for each serving cell. Each transport block and HARQ retransmission are mapped to a single serving cell.
In a case where CA is configured, a UE has single RRC connection with a NW. In RRC connection, one serving cell provides NAS mobility information and security input. This cell is referred to as primary cell (PCell). In downlink, a carrier corresponding to PCell is a downlink primary component carrier (DL PCC). In uplink, a carrier corresponding to PCell is an uplink primary component carrier (UL PCC).
A secondary cell (SCell) is configured to form a pair of a PCell and a serving cell, in accordance with the UE capability. In downlink, a carrier corresponding to SCell is a downlink secondary component carrier (DL SCC). In uplink, a carrier corresponding to SCell is an uplink secondary component carrier (UL SCC).
A pair of one PCell and a serving cell configured by one or more SCells is configured for one UE.
In each SCell, a UE is capable of using resources for uplink (UL) in addition to resources for downlink (DL). The number of DL SCCs is equal to or more than the number of UL SCCs. No SCell is used for only resources for UL. Each resource for UL belongs to only one serving cell for one UE. The number of serving cells depends on the UE capability.
The PCell is changed through only a HO procedure. The PCell is used for transmission of PUCCH. The PUCCH for HARQ of the DL-SCH without UL-SCH is transmitted through only UL PCC. Differently from SCells, the PCell is not de-activated.
Re-establishment is triggered when the PCell results in a radio link failure (RLF). Re-establishment is not triggered in a case of SCells. The NAS information is obtained from the PCell.
The SCells are reconfigured, added, or removed through RRC. Also in handover within the LTE, the SCells used together with a target PCell are added, removed, or reconfigured through RRC.
In a case of SCell addition, dedicated RRC signaling is used to transmit the all system information (SI) required for the SCell. That is, addition is performed in a connected mode, and the UE does not have to receive the SI broadcast from the SCell.
It is studied that a PCell notifies user equipments of SCell addition/modification using “RRC Connection Reconfiguration message” of dedicated RRC signaling (see Non-Patent Document 2). It is studied that SCell release is notified UEs by a PCell using “RRC Connection Reconfiguration message” of dedicated RRC signaling or is triggered by “RRC Connection re-establishment” (see Non-Patent Document 2). “RRC Connection Reconfiguration message” of dedicated RRC signaling contains “SCell To AddModList” and “SCell To ReleaseList”.
In each cell, the SIB2 represents a carrier frequency of a resource for uplink.
Local nodes are installed for complementing a macro cell in response to demands for various services such as high-speed and high-capacity communication. Accordingly, the local node may be installed within the coverage of the macro cell. In this case, an interference may occur from a user equipment to the local node.
A case in which a local node is a remote radio head (RRH) and the coverage of the macro cell is larger than the coverage of the RRH, that is, a case in which the downlink transmission power of the macro cell is larger than the downlink transmission power of the RRH is considered here as a specific example. The downlink reception power of the user equipment at each point becomes smaller as the distance from each node increases. The uplink transmission power of the user equipment to each node needs to be increased as the distance from each node increases.
The user equipment according to the conventional technique camps on a cell having the best downlink reception quality, and thereafter, starts communication as required (see Non-Patent Document 3). In areas where the downlink reception power from the macro cell is larger than the downlink reception power from the RRH, the user equipment camps on the macro cell and performs uplink transmission to the macro cell.
In the area where the uplink transmission power from the user equipment to the macro cell is larger than the uplink transmission power from the user equipment to the RRH among the above-mentioned areas, the link between the UE and RRH is better than the other link in uplink, whereas the link between the UE and macro cell is better than the other link in downlink. As described above, an imbalance in link, that is, a link imbalance occurs.
When a link imbalance occurs, an interference occurs from the user equipment to the RRH due to relatively large uplink transmission power from the user equipment to the macro cell. Due to this interference, the communication between the user equipment and macro cell or the communication between the user equipment and RRH is hindered, leading to a reduction in throughput of the entire communication system. Therefore, there is required a method of reducing an interference occurring in a HetNet being a heterogeneous network in which a macro cell and a local node coexist, to thereby improve a throughput of the entire communication system.
Non-Patent Document 10 discloses a solution to the inter-cell interference problem in a heterogeneous network. Specifically, the use of a radio link exclusively in uplink and downlink during the communication of a user equipment is disclosed as a solution. In this solution, the same frequency is used in the respective cells.
Non-Patent Document 11 also discloses a solution to the inter-cell interference problem in a heterogeneous network. Specifically, the following solutions are disclosed: carrier aggregation is performed in each cell with different carrier frequencies between the macro cell and pico cell, and the user equipment accesses the pico cell when the user equipment comes closer to the pico cell. However, Non-Patent Document 11 does not disclose the details of the method in which the user equipment accesses the pico cell when the user equipment comes closer to the pico cell.
Non-Patent Document 1 discloses several scenarios regarding carrier aggregation. Among the scenarios disclosed in Non-Patent Document 1, scenario 4 discloses that the RRH operating on a frequency 2 (F2) is aggregated with the macro cell operating on a frequency 1 (F1).